Exhaust-gas purifying device

ABSTRACT

An exhaust-gas purifying device purifies an exhaust gas exhausted from a gasoline engine of a vehicle and flowing in an exhaust pipe, and has a purifying function part disposed in the exhaust pipe and a detector located downstream of the purifying part in the exhaust pipe. The purifying function part has a three-way catalyst that oxidizes and reduces a toxic substance and a filter that collects a particular matter included in the exhaust gas. The detector detects an amount of the particular matter based on electrical conductivity between the electrodes of the detector. The detector is located at a position that is one meter distanced from a downstream end of the purifying function part in a path length of the exhaust pipe or a position at which a temperature of the exhaust gas flowing after a warm-up operation of the gasoline engine is lower than or equal to 450° C.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2015-016205 filed on Jan. 30, 2015, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an exhaust-gas purifying device that purifies exhaust gas exhausted from a gasoline engine of a vehicle and flowing in an exhaust pipe.

BACKGROUND ART

A particulate matter (Particle matter: PM) emitted from an internal combustion engine with exhaust gas is required to be reduced recently, and therefore lows and regulations are being tightened. For reducing the particulate matter, an air-fuel ratio in a cylinder of the internal combustion engine may be controlled to reduce a production amount of the particulate matter. However, the lows and regulations require the particulate matter to be reduced not only in weight but also in quantity. A measure for reducing the production amount of the particulate matter alone may not be able to response to lows and regulations, which will be established in the future, with a high probability.

Patent Literature 1 discloses a device for removing a particulate matter by disposing a filter in a passage in which exhaust gas flows. The filter removes the particulate matter from the exhaust gas by collecting the particulate matter flowing through the filter. The measure using the filter removes the particulate matter efficiently, and thereby is used widely.

The device disclosed in Patent Literature 1 further has a detector located downstream of the filter and performs a failure decision of the filter by the detector. The detector has an electrical insulating portion and electrodes, and is configured such that an electrical resistance between the electrodes is changed depending on an amount of the particulate matter attached to the electrical insulating portion. The electrical resistance falls as an attachment of the particulate matter to the electrical insulating portion advances. Then, the filter is determined to be broken and not to be performing a collection of the particulate matter appropriately, when the electrical resistance becomes smaller than a reference value.

Here, the device disclosed in Patent Literature 1 removes the particulate matter, as a target to be removed, emitted from a diesel engine. A device for the gasoline engine thereby may be possible to remove the particulate matter by the filter and to perform the failure decision by the detector.

PRIOR ART LITERATURES Patent Literature

Patent Literature 1: JP 2009-144577 A

SUMMARY OF INVENTION

However, according to studies conducted by the inventor of the present disclosure, a gasoline engine has different characteristics as compared to a diesel engine, and it is not easy for a device for a gasoline engine to remove the particulate matter by the filter. Challenges in the above-described issue will be described hereafter in detail.

Exhaust gas hardly flow through a filter when a particulate matter deposits on the filter excessively, and thereby fuel economy of the gasoline engine is decreased. Accordingly, a recovery processing in which the particulate matter collected by the filter is burnt and removed to recover a function of the filter is required to be performed before the particulate matter deposits on the filter excessively.

However, an amount of oxygen in the exhaust gas exhausted from the gasoline engine is small as compared to that from the diesel engine since fuel (i.e., gasoline) is burnt on a condition that an air-fuel ratio is close to the theoretical air-fuel ratio in the gasoline engine. As a result, the particulate matter deposited on the filter may not be burnt sufficiently, and thereby the recovery processing may not be performed appropriately.

In addition, the amount of oxygen included in the exhaust gas flowing to the filter becomes even smaller when a three-way catalyst is disposed upstream of the filter, since the three-way catalyst uses the oxygen included in the exhaust gas for an oxidation reaction. As a result, it becomes even harder to burn the particular matter deposited on the filter. On the other hand, a long period of time may be required for an activation of the three-way catalyst using heat of the exhaust gas in a warm-up operation of the gasoline engine, on a condition that the three-way catalyst is disposed downstream of the filter.

Then, a measure that increases the amount of oxygen included in the exhaust gas emitted from the gasoline engine and flowing to the filter is considered. According to the measure, for example, the amount of oxygen is increased by controlling the air-fuel ratio to reduce a fuel supply to the gasoline engine temporary, such that the fuel is burnt on a condition that the air-fuel ratio is larger than the theoretical air-fuel ratio.

However, a temperature of the exhaust gas exhausted by the gasoline engine tends to be higher than a temperature of the exhaust gas exhausted by the diesel engine. Accordingly, the above-described detector is heated by the exhausted gas, and a temperature of the detector may become high. In addition, the particular matter deposited on the detector may be burnt spontaneously when an amount of oxygen, which is included in the exhaust gas supplied to the detector, is increased by controlling the air-fuel ratio. As a result, the detector may not be able to perform the failure decision of the filter accurately.

The present disclosure addresses the above-described issues, and it is an object of the present disclosure to provide an exhaust-gas purifying device that purifies exhaust gas exhausted by a gasoline engine for a vehicle and flowing in an exhaust pipe and that can detect an amount of a particular matter included in the exhaust gas after passing through a filter while performing a recovery processing of the filter.

An exhaust-gas purifying device according to the present disclosure purifies an exhaust gas exhausted from a gasoline engine of a vehicle and flowing in an exhaust pipe. The exhaust-gas purifying device has a purifying function part and a detector. The purifying function part is disposed in the exhaust pipe and has a three-way catalyst and a filter. The three-way catalyst oxidizes and reduces a toxic substance included in the exhaust gas by a metal catalytic agent. The filter collects a particular matter that is included in the exhaust gas flowing through the filter. The detector is disposed in the exhaust pipe and located downstream of the purifying part in the exhaust pipe. The detector has an electrical insulating portion to which the particular matter attached and electrodes arranged to be distanced from each other. The detector detects an amount of the particular matter attached to the electrical insulating portion based on electrical conductivity between the electrodes. The detector is located at a position that is one meter distanced from a downstream end of the purifying function part in a path length of the exhaust pipe or a position at which a temperature of the exhaust gas flowing after a warm-up operation of the gasoline engine is lower than or equal to 450° C.

According to the present embodiment, the detector is located at a position that is one meter distanced from a downstream end of the purifying function part in a path length of the exhaust pipe or a position at which a temperature of the exhaust gas flowing after a warm-up operation of the gasoline engine is lower than or equal to 450° C. A temperature at which a common particular matter generated in combustion of gasoline starts burning spontaneously is about 500° C. In addition, a temperature of exhaust gas exhausted from a gasoline engine mounted in a vehicle is lower than 500° C. commonly, at a position that is one meter or longer distanced from a downstream end of a function part in a path length of an exhaust pipe. Thus, according to the present embodiment, the particular matter attached to the detector can be prevented from burning spontaneously, and an amount of the particular matter included in the exhaust gas after passing through the filter can be detected, even when an amount of oxygen included in the exhaust gas flowing to the detector is increased by controlling an air-fuel ratio in a recovery processing of the filter.

According to the present disclosure, an exhaust-gas purifying device that purifies exhaust gas exhausted by a gasoline engine for a vehicle and flowing in an exhaust pipe and that can detect an amount of a particular matter included in the exhaust gas after passing through a filter while performing a recovery processing of the filter can be provided.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings.

FIG. 1 is a schematic diagram illustrating a vehicle in which an exhaust-gas purifying device according to a first embodiment is mounted.

FIG. 2 is a schematic diagram illustrating a PM sensor shown in FIG. 1.

FIG. 3 is a schematic diagram showing a temperature variation of exhaust gas in the vehicle shown in FIG. 1.

FIG. 4 is a schematic diagram illustrating a sectional view of a filter shown in FIG. 1.

FIG. 5 is a schematic diagram showing a temperature variation of exhaust gas in a vehicle in which an exhaust-gas purifying device according to a second embodiment is mounted.

FIG. 6 is a cross-sectional view of a surface of a filter shown in FIG. 5.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described hereinafter referring to drawings. In the embodiments, a part that corresponds to or equivalents to a part described in a preceding embodiment may be assigned with the same reference number, and a redundant description of the part may be omitted. When only a part of a configuration is described in an embodiment, another preceding embodiment may be applied to the other parts of the configuration. The parts may be combined even if it is not explicitly described that the parts can be combined. The embodiments may be partially combined even if it is not explicitly described that the embodiments can be combined, provided there is no harm in the combination.

First Embodiment

An exhaust-gas purifying device CA1 according to a first embodiment will be described hereafter referring to FIG. 1 through FIG. 4. The exhaust-gas purifying device CA1 is a device that purifies exhaust gas exhausted from a gasoline engine 100 (referred to as the engine 100 hereafter) mounted in a vehicle GC. A configuration of the vehicle GC will be described referring to FIG. 1.

In FIG. 1, the engine 100 and a peripheral configuration thereof in the vehicle GC is illustrated schematically, and illustrations of other configurations are omitted. As shown in FIG. 1, the vehicle GC has the engine 100, an intake pipe 200, and an exhaust pipe 300.

The engine 100 is a gasoline engine having four cylinders 101. According to the present embodiment, the engine 100 is a direct-injection internal combustion engine that injects gasoline, as a fuel, directly into a combustion chamber 102. The four cylinders 101 have the same configuration and are controlled in the same manner, therefore one cylinder 101 will be illustrated and described hereafter.

The cylinder 101 has an intake valve 151, an exhaust valve 152, an opening/closing adjustment mechanism 190, a spark plug 160, a piston 170, and an injector 180. The cylinder 101 defines a combustion chamber 102 therein. The combustion chamber 102 is a space in which a mixed gas of fuel and air burns.

The intake valve 151 is disposed in a connecting portion in which the intake pipe 200 and the cylinder 101 are coupled. An air supply to the combustion chamber 102 is started when the intake valve 151 is open. The air supply to the combustion chamber 102 is stopped when the intake valve 151 is closed.

The exhaust valve 152 is disposed in a connecting portion in which the exhaust pipe 300 and the cylinder 101 are coupled. An exhaust of exhaust gas from the combustion chamber 102 to the exhaust pipe 300 is started when the exhaust valve 152 is open. The exhaust of the exhaust gas from the combustion chamber 102 to the exhaust pipe 300 is stopped when the exhaust valve 152 is closed.

The opening/closing adjustment mechanism 190 opens and closes the intake valve 151 and the exhaust valve 152. The opening/closing adjustment mechanism 190 opens and closes the intake valve 151 and the exhaust valve 152 at appropriate timing, and thereby an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke are performed in the cylinder 101.

The opening/closing adjustment mechanism 190 is configured as a variable valve timing mechanism provided with VVT (registered trademark) pulley (not shown). Accordingly, the timing for opening and closing the intake valve 151 and the exhaust valve 152 is not fixed consistently, and the opening/closing adjustment mechanism 190 can change the timing while the intake stroke, the compression stroke, the combustion stroke, and the exhaust stroke are performed.

Specifically, the opening/closing adjustment mechanism 190 can adjust a gap (i.e., an overlap) between a timing at which the exhaust valve 152 is closed to complete the exhaust stroke and a timing at which the intake valve 151 is open to start the intake stroke. The intake valve 151 and the exhaust valve 152 are controlled to be open and closed by a controller 400.

The spark plug 160 is an ignition device that performs a spark ignition and ignitions the mixed air of the fuel and the air in the combustion chamber 102. The controller 400 controls a timing (i.e., an ignition timing) at which the spark plug 160 performs the spark ignition, i.e., a timing at which the combustion stroke is started.

The piston 170 is a member moving back and forth in an up-down direction in the cylinder 101. The combustion chamber 102 defines an upper area, located above the piston 170, of the space defined inside the cylinder.

In the compression stroke, the piston 170 moves upward, and a volume of the combustion chamber 102 decreases. In the combustion stroke, the piston 170 is pushed to move downward by a combustion (i.e., an explosion) of the fuel caused in the combustion chamber 102. A connecting rod 171 and crankshaft 172 are arranged below the piston 170. A moving direction of the piston 170 moving back and force is changed by a rotational movement of the crankshaft 173 etc. Accordingly, explosion power generated in the combustion chamber 102 is converted into driving force for driving the vehicle GC.

The injector 180 is an on-off valve for injecting the fuel directly into the combustion chamber 102. The controller 400 controls a timing at which the injector 180 starts a fuel supply to the combustion chamber 102 and a volume of the fuel supplied into the combustion chamber 102.

The intake pipe 200 is a pipe for supplying air to the cylinder 101. A throttle valve (not shown) is disposed in the intake pipe 200. The throttle valve is open and closed when a driver operates an accelerator, and thereby a volume of air supplied to the cylinder 101 is adjusted.

The exhaust pipe 300 is a manifold pipe. Exhaust gases flowing out of the cylinders 101 join together and flow in the exhaust pipe 300. The exhaust pipe 300 guides the exhaust gases to an outside of the vehicle GC. A purifying function part 10 and a PM sensor 14 (i.e., a detector) are disposed in the exhaust pipe 300. The purifying function part 10 has a three-way catalyst 11 and a filter 12.

The three-way catalyst 11 has a honeycomb shape or the like and is configured to guides the exhaust gas flowing in the exhaust pipe 300 to pass through the three-way catalyst 11. The three-way catalyst 11 has a catalytic carrier (not shown) supporting platinum, palladium, and rhodium that are metal catalytic agents. The three-way catalyst 11 purifies the exhaust gas by oxidizing or reducing a toxic substance (hydrocarbon, carbon monoxide, and nitrogen oxide) included in the exhaust gas using catalytic actions of the metal catalytic agents.

The filter 12 is disposed in the exhaust pipe 300 and located downstream of the three-way catalyst 11. The filter 12 has a honeycomb shape or the like and is configured to guides the exhaust gas flowing from the three-way catalyst 11 to pass through the filter 12. The filter 12 may be referred to as Gasoline Particle Filter (GPF).

As shown in FIG. 4, the filter 12 has partition walls 123 arranged to be distanced from each other. The partition walls 123 is made of porous ceramics of which average pore diameter is smaller than or equal to 80 μm. The partition walls 123 configure a honeycomb structural body as a whole. The partition walls 123 define inlet-sealed cells 125 and penetration cells 126 that respectively extend from an upstream end 121 of the filter 12 to a downstream end 122 of the filter 12. The inlet-sealed cells 125 are open at the downstream end 122 of the filter 12 and are sealed by sealing portions 124 respectively at the upstream end 121 of the filter 12. The penetration cells 126 pass through the filter 12 from the upstream end 121 to the downstream end 122. The inlet-sealed cells 125 and the penetration cells 126 are arranged alternately with each other in the filter 12.

According to the above-described configuration, the exhaust gas flows into the penetration cells 126 of the filter 12 first. A pressure inside the penetration cells 126 increases while the exhaust gas flows in the penetration cells 126 toward the downstream end 122. On the other hand, the exhaust gas does not flow into the inlet-sealed cells 125 from the upstream end 121 since the sealing portion 124 seal the inlet-sealed cells 125 respectively. As a result, a pressure inside the inlet-sealed cells 125 is lower than the pressure inside the penetration cells 126.

Since the pressure inside the inlet-sealed cells 125 is lower than the pressure inside the penetration cells 126, the exhaust gas flowing in the penetration cells 126 flows into the inlet-sealed cells 125 through the partition walls 123. The partition walls 123 collect the particular matter PM included in the exhaust gas, and thereby the particular matter PM is removed from the exhaust gas, while the exhaust gas flows through the partition walls 123. The exhaust gas flows out of the filter 12 from the downstream end 122 after the particular matter PM is removed from the exhaust gas. Since the inlet-sealed cells 125 and the penetration cells 126 are open at the downstream end 122, a dramatic increase of a pressure loss can be suppressed even when an amount of the particular matter PM collected by the partition walls 123 increases.

As shown in FIG. 3, the PM sensor 14 is disposed in the exhaust pipe 300 and located downstream of the filter 12. The PM sensor 14 detects an amount of the particular matter PM included in the exhaust gas after passing through the filter, as described later. The PM sensor 14 is electrically connected to the controller 400 and sends the controller 400 a signal corresponding to a detection amount of the particular matter PM.

A configuration of the PM sensor 14 will be described hereafter referring to FIG. 2. The PM sensor 14 has an electrical insulation portion 141, an electrode 142 a, an electrode 142 b, and an indicator 143.

The electrical insulation portion 141 is made of a material such as alumina. The electrical insulation portion 141 is arranged to be exposed to the exhaust gas flowing in the exhaust pipe 300 as shown in arrow F.

The electrodes 142 a, 142 b are made of metal. Each of the electrodes 142 a, 142 b has a portion located inside the electrical insulation portion 141 and another portion protruding from a surface of the electrical insulation portion 141. The electrode 141 a and the electrode 142 a are distanced from each other on the surface of the electrical insulation portion 141.

The indicator 143 is electrically connected to the electrode 142 a and the electrode 142 b and measures an electrical resistance between the electrode 142 a and the electrode 142 b. Specifically, the indicator 143 applies a measured voltage between the electrode 142 a and the electrode 142 b and measures the electrical resistance based on a value of current caused by the measured voltage.

A failure decision performed by the PM sensor 14 to determine whether the filter 12 is broken will be described hereafter. The filter 12 does not collect the particular matter PM appropriately when the filter 12 is broken, e.g., is damaged by being melted. Accordingly, the particular matter PM is not removed while the exhaust gas passes through the filter 12, and the exhaust gas flows to the PM sensor 14 located downstream of the filter 12.

The particular matter PM reaching the PM sensor 14 with the exhaust gas is attached to the surface of the electrical insulation portion 141 of the PM sensor 14. The particular matter PM has a greater electrical conductivity with respect to the electrical insulation portion 141. Accordingly, the electrical resistance between the electrode 142 a and the electrode 142 b measured by the indicator 143 decreases as an amount of the particular matter PM attached to the electrical insulation portion 141 increases. The controller 400 can determine the filter 12 to be broken when the electrical resistance measured by the PM sensor 14 is smaller than or equal to a threshold value.

The particular matter PM deposits to the filter 12. The exhaust gas hardly flows through the filter 12 when the particular matter PM deposits to the filter 12 excessively, and thereby fuel economy of the engine 100 may be decreased. Accordingly, the particular matter PM collected by the filter 12 is required to be burnt and to be removed from the filter 12 such that a recovery processing for recovering a function of the filter 12 is performed, before the particular matter PM deposits to the filter 12 excessively.

Commonly, an amount of oxygen included in exhaust gas exhausted from a gasoline engine is smaller than an amount of oxygen included in exhaust gas exhausted from a diesel engine. Accordingly, the amount of oxygen may be insufficient for burning the particular matter PM in the filter 12. Then, a measure that increases the amount of oxygen included in the exhaust gas emitted from the engine 100 and flowing to the filter 12 is considered. According to the measure, for example, the amount of oxygen is increased by controlling the air-fuel ratio to reduce a fuel supply to the engine 100 temporary, such that the fuel is burnt on a condition that the air-fuel ratio is larger than the theoretical air-fuel ratio.

However, a temperature of the exhaust gas exhausted from the gasoline engine tends to be higher than a temperature of the exhaust gas exhausted from the diesel engine. Accordingly, the PM sensor 14 is heated by the exhausted gas, and a temperature of the PM sensor 14 may become high. In addition, the particular matter PM deposited on the electrical insulation portion 141 of the PM sensor 14 may be burnt spontaneously when the amount of oxygen, which is included in the exhaust gas supplied to the PM sensor 14, is increased by controlling the air-fuel ratio. As a result, the PM sensor 14 may not be able to perform the failure decision of the filter 12 accurately.

Then, according to the first embodiment, an arrangement of the purifying function part 10 and the PM sensor 14 in the exhaust-gas purifying device CA1 is considered to prevent the above-described abnormalities from being caused. The arrangement will be described hereafter referring to FIG. 3.

As shown in FIG. 3, the exhaust pipe 300 having a manifold configuration is connected to the engine 100, and the purifying function part 10 and the PM sensor 14 are disposed in the exhaust pipe 300. The exhaust pipe 300 has a header 301, a collector 302, a housing portion 303, and an exhaust portion 304.

The exhaust pipe 300 is bent actually to fit a shape of the engine 100 and a shape of an engine room of the vehicle GC, however is illustrated to extend straight for an explanation purpose.

FIG. 3 also shows a temperature of the exhaust gas flowing in various portions of the exhaust pipe 300. In the graph, the origin is the upstream end of the exhaust pipe 300 at which the exhaust pipe 300 is connected to the cylinders 101 of the engine 100, the horizontal axis is a distance from the origin, and the vertical axis is the temperature of the exhaust gas.

The purifying function part 10 is housed in the housing portion 303 that is located downstream of the collector 302 and has a larger inside diameter as compared to that of the collector 302. The three-way catalyst 11 is located at a position, a distance at which from the origin is between L11 and L12. The filter 12 is distanced from a downstream end 112 of the three-way catalyst 11 and located at a position, a distance at which from the origin is between L13 and L14.

The PM sensor 14 is located downstream of the housing portion 303 and is located in the exhaust portion 304 that has a smaller inside diameter as compared to the collector 302. The PM sensor 14 is located at a position, a distance at which from the origin is L15.

The combustion stroke and the exhaust stroke are performed in different phases in the cylinders 101 of the engine 100. Accordingly, exhaust gasses having a high temperature flow into the header 301 from the cylinders 101 at different timings respectively.

The exhaust gasses after passing through the header 301 join together in the collector 302 located downstream of the header 301 and flow to a downstream side of the collector 302. The exhaust gas radiates heat outside through a wall configuring the header 301 and the collector 302 while flowing through the header 301 and the collector 302, and thereby a temperature of the exhaust gas falls gradually. As a result, a temperature of the exhaust gas, which is T17 when flowing in the header 301, falls to T12 when reaching an upstream end 111 of the three-way catalyst 11.

The three-way catalyst 11 is preferably located at a position at which the exhaust gas having a high temperature flows into the three-way catalyst 11, such that catalytic actions of the metal catalytic agents are activated. On the other hand, the three-way catalyst 11 may be damaged by heat of the exhaust gas when a temperature of the exhaust gas flowing into the three-way catalyst 11 is excessively high. The above-described requirements and restrictions are considered, and thereby the three-way catalyst 11 is located at a position at which the exhaust gas having an appropriate temperature (e.g., T12) flows into the three-way catalyst 11, i.e., at a position, a distance at which from the origin is L11.

The metal catalytic agents oxidize or reduce the toxic substance included in the exhaust gas flowing into the three-way catalyst 11 while the exhaust gas flows through the three-way catalyst 11. The oxidization and the reduction generate heat, and therefore a temperature of the exhaust gas passing through the three-way catalyst 11 increases to T16. The oxidization and the reduction of the toxic substance included in the exhaust gas are almost completed in an upstream portion of the three-way catalyst 11. Therefore, a temperature of the exhaust gas falls slightly in a downstream portion of the three-way catalyst 11, and becomes T15 when flowing out of the downstream end 112 (i.e., a position, a distance at which from the origin is L12).

The exhaust gas, after passing through the three-way catalyst 11, flows into the filter 12 subsequently. The exhaust gas radiates heat outside through the wall configuring the housing portion 303 while flowing from the downstream end 112 of the three-way catalyst 11 to the upstream end 121 of the filter 12, and thereby a temperature of the exhaust gas falls from T15 to T14.

The filter 12 is preferably located at a position at which the exhaust gas having a high temperature flows into the filter 12 such that the recovery processing in which the particular matter PM collected by the filter is burnt is performed certainly. Therefore, the filter 12 is located at a position that is 0.5 meter distanced from the downstream end 112 of the three-way catalyst 11. That is, the filter 12 is located such that a difference between L12 and L13 is within 0.5 meter. Accordingly, the exhaust gas of which temperature is increased by the oxidization and the reduction performed while the exhaust gas passes through the three-way catalyst 11 flows into the filter 12, the particular matter PM is burnt by heat from the exhaust gas, and thereby the recovery processing can be performed certainly.

From the same point of view, the filter 12 may be located downstream of the downstream end 112 of the three-way catalyst 11 at a position at which a temperature of the exhaust gas falls to be lower than or equal to 50° C. after the warm-up operation of the engine 100 and after the activation of the three-way catalyst 11. That is, the filter 12 may be located at a position at which a difference between T15 and T14 is smaller than or equal to 50° C. after the warm-up operation of the engine 100 and after the activation of the three-way catalyst 11.

The filter 12 adsorbs heat from the exhaust gas passing through the filter 12, and thereby a temperature of the exhaust gas decreases. Thus, the temperature of the exhaust gas decreases from T14 to T13 while the exhaust gas flows from the upstream end 121 to the downstream end 122 in the filter 12.

The exhaust gas, which passes through the filter 12 and flows out of the housing portion 303 of the exhaust pipe 300, is guided to a portion in which the PM sensor 14 by the exhaust portion 304. Meanwhile a temperature of the exhaust gas decreases gradually since the exhaust gas radiates heat outside through the wall of the guide portion 304. Accordingly, the temperature of the exhaust gas is T11 at a position in which the PM sensor 14 is disposed (i.e., at a position, a distance at which from the origin is L15).

Here, the PM sensor 14 is preferably disposed at a position where the exhaust gas of which temperature is decreased sufficiently flows, such that the particular matter PM attached to the electrical insulation portion 141 does not burn spontaneously. The particular matter PM generated by combustion of a common gasoline starts burning spontaneously at about 500° C. Therefore, the PM sensor 14 is located at a position in which T11 becomes lower than or equal to 450° C. Thus, the particular matter PM attached to the PM sensor 14 can be prevented from burning spontaneously, and thereby the PM sensor 14 can detects the amount of the particular matter PM included in the exhaust gas after passing through the filter 12, even when the amount of oxygen in the exhaust gas supplied to the PM sensor 14 increases by controlling the air-fuel ratio in the recovery processing of the filter 12.

From the same point of view, the PM sensor 14 may be located at a position 1 meter or longer distanced from the downstream end of the purifying function part 10 (i.e., the downstream end 122 of the filter 12). That is, the PM sensor 14 may be arranged such that a distance between L14 and L15 is smaller than or equal to 1 meter. The reasons for arranging the PM sensor 14 at such a position is that the temperature of the exhaust gas is lower than 500° C. at a position 1 meter or longer distanced from the downstream end of the purifying function part in the path length of the exhaust pipe in the gasoline engine mounted in a vehicle.

Moreover, the engine 100 is set to rotate at a rotation speed lower than or equal to 4,000 rpm in the normal operation range preferably. It is extremely difficult to control the temperature of the exhaust gas as described above at every rotation speed of the engine 100, at the position where the purifying function part 10 and the PM sensor 14 are disposed. However, in a common vehicle, a high performance of the exhaust-gas purifying device CA1 can be obtained simultaneously making the above-described temperature control easy, by setting the normal operation range, in which the engine operates frequently in the common vehicle, to be a range in which the rotation speed is lower than or equal to 4,000 rpm.

In addition, the filter 12 has the inlet-sealed cells 125 and the penetration cells 126 arranged alternately with each other. The upstream ends of the inlet-sealed cells 126 are sealed, and the downstream ends of the inlet-sealed cells 126 are open such that the exhaust gas flows out of the downstream ends. The penetration cells 126 penetrate the filter 12 from the upstream end to the downstream end, and the exhaust gas flows in the penetration cells 126. By using the filter 12 having the above-described configuration, the particular matter PM can be removed from the exhaust gas without increasing the pressure loss dramatically even when the amount of the particular matter PM collected by the filter 12 increases. Particularly, as shown in FIG. 3, an increase of the pressure in the exhaust pipe 300 on an upstream side of the three-way catalyst 11 can be suppressed even when the filter 12 is arranged adjacent to the downstream end 112 of the three-way catalyst 11. Thus, the particular matter PM can be removed from the exhaust gas while suppressing a power reduction of the engine.

Second Embodiment

An exhaust-gas purifying device CA2 according to a second embodiment will be described hereafter referring to FIG. 5 and FIG. 6. Similar to the exhaust-gas purifying device CA1, the exhaust-gas purifying device CA2 is a device that purifies the exhaust gas emitted from the engine 100 mounted in the vehicle GC. Accordingly, the same part as the exhaust-gas purifying device CA1 is assigned with the same reference number, and descriptions thereof will be omitted.

The purifying function part 10 of the exhaust-gas purifying device CA2 is configured only by a filter 13. However, as shown in FIG. 6, metal catalytic agents 136 made of a material such as platinum, palladium, and rhodium is held on a surface of a base body 134 by a binder 135. The base body 134 configures an outer shape of the filter 13. The filter 13 collects the particular matter PM and removes the particular PM from the exhaust gas passing through the filter 13, and oxidizes or reduces the toxic substance in the exhaust gas by catalytic actions of the metal catalytic agent 136.

That is, the filter 13 has both of a function as the above-described three-way catalyst 11 and a function as the filter 12. As shown in FIG. 5, the filter 13 is located at a portion, a distance at which from the origin is between L21 and

L22.

Exhaust gasses after passing through the header 301 are mixed with each other in the collector 302 located downstream of the header 301, and flow to a downstream side of the collector 302. The exhaust gas radiates heat to outside through the wall of the header 301 and the collector 302 while flowing in the header 301 and the collector 302, and thereby a temperature of the exhaust gas decreases gradually. Accordingly, the temperature of the exhaust gas is T25 when the exhaust gas flows into the header 301, and falls to T22 before the exhaust gas reaches an upstream end 131 of the filter 13.

The filter 13 is preferably located at a position to which the exhaust gas having a high temperature flows, from a point of view of activating the catalytic actions of the metal catalytic agents 136 and performing the recovery processing in which the particular matter PM collected by the filter 13 is burnt. On the other hand, the filter 13 may be damaged by heat from the exhaust gas when the temperature of the exhaust gas flowing into the filter 13 is extremely high. In consideration of the above-described requirements and restrictions, the filter 13 is located at a position (i.e., a position, a distance at which from the origin is L21) to which the exhaust gas having an appropriate temperature (T22) flows.

The filter 13 oxidizes or reduces the toxic substance in the exhaust gas flowing into the filter 13 by the metal catalytic agents 136 while the exhaust gas passes through the filter 13. The oxidization and the reduction generate heat, thereby increasing the temperature of the exhaust gas being passing through the filter 13 to T24. The oxidization and the reduction of the toxic substance in the exhaust gas are almost completed in an upstream portion of the filter 13. Therefore, the temperature of the exhaust gas slightly falls in a downstream portion of the filter 13, and becomes T23 before flowing out of a downstream end 132 (i.e., before flowing out of a position, a distance at which from the origin is L22).

The exhaust portion 304 guides the exhaust gas, after passing through the filter 13 and flowing out of the housing portion 303 of the exhaust pipe 300, to the portion in which the PM sensor 14 is disposed. Meanwhile, the exhaust gas radiates heat through the wall of the guide portion 304, and thereby a temperature of the exhaust gas decreases gradually. Accordingly, the temperature of the exhaust gas is T21 at the position in which the PM sensor 14 is disposed (i.e., at a position, a distance at which from the origin is L23).

The PM sensor 14 is preferably disposed at a position where the exhaust gas of which temperature is decreased sufficiently flows, such that the particular matter PM attached to the electrical insulation portion 141 does not burn spontaneously, according to the exhaust-gas purifying device CA2 of the second embodiment, similarly to the first embodiment. Therefore, the PM sensor 14 is located at a position at which T21 is loser than or equal to 450° C.

In the same point of view, the PM sensor 14 may be located at a position that is one meter or longer distanced from the downstream end of the purifying function part 10 (i.e., the downstream end 132 of the filter 13). That is, the PM sensor 14 may be located such that a difference between L22 and L23 is within one meter.

(Other Modifications)

The embodiments of the present disclosure are described above referring to specific examples, however the present disclosure is not limited to the specific examples. That is, modifications that are made as required by a person having ordinary skill in the art based on the specific examples are included in a range of the present disclosure as long as having the features of the present embodiment. For example, elements mentioned in the specific examples, an arrangement, a material, a condition, a shape, a size, etc. of the elements are not limited to the specific examples, and can be changed as required. The elements mentioned in the specific examples can be combined as long as it is technically possible, and the combination is included in the range of the present disclosure as long as having the features of the present embodiment.

For example, the PM sensor 14 refers the electrical resistance as an index of electrical conductivity between the electrode 142 a and the electrode 142 b according to the above-described embodiments. However, the amount of the particular matter PM may be detected based on current flowing between the electrode 142 a and the electrode 142 b or a potential difference between the electrode 142 a and the electrode 142 b, instead of the electrical resistance, or in addition to the electrical resistance. 

1. An exhaust-gas purifying device that purifies an exhaust gas exhausted from a gasoline engine of a vehicle and flowing in an exhaust pipe, the exhaust-gas purifying device comprising: a purifying function part that is disposed in the exhaust pipe and has a three-way catalyst and a filter, the three-way catalyst oxidizing and reducing a toxic substance included in the exhaust gas by a metal catalytic agent, the filter collecting a particular matter that is included in the exhaust gas flowing through the filter; and a detector that is disposed in the exhaust pipe and located downstream of the purifying part in the exhaust pipe, the detector that has an electrical insulating portion to which the particular matter is attached and a plurality of electrodes arranged to be distanced from each other, the detector that detects an amount of the particular matter attached to the electrical insulating portion based on electrical conductivity between the plurality of electrodes, wherein the detector is located at a position that is one meter distanced from a downstream end of the purifying function part in a path length of the exhaust pipe, or at a position at which a temperature of the exhaust gas flowing after a warm-up operation of the gasoline engine is lower than or equal to 450° C.
 2. The exhaust-gas purifying device according to claim 1, wherein the three-way catalyst is disposed in the exhaust pipe separately from the filter and located upstream of the filter, and the filter is located at a position that is 0.5 meter distanced from the downstream end of the three-way catalyst in the path length of the exhaust pipe, or at a position at which a temperature of the exhaust gas flowing out of the downstream end of the three-way catalyst is lower than or equal to 50° C. after the warm-up operation of the gasoline engine and after an activation of the three-way catalyst.
 3. The exhaust-gas purifying device according to claim 1, wherein the metal catalytic agent is supported on a surface of the filter.
 4. The exhaust-gas purifying device according to claim 1, wherein a rotation speed of the gasoline engine is lower than or equal to 4,000 rpm in a normal operation range.
 5. The exhaust-gas purifying device according to claim 1, wherein the filter has a penetration cell that passes through the filter from an upstream end to a downstream end of the filter, the penetration cell in which the exhaust gas flows, and an inlet-sealed cell that is located adjacent to the penetration cell and has an upstream opening being sealed and a downstream opening being opened, the exhaust gas that flows out of the downstream opening of the inlet-sealed cell. 